Carrier supply system



"J'Qs, i938.

R. D. DUNCAN, JR

CARRIER SUPPLY 'SYS TEM Filed Aug. l, 1936 wrm. IIIIIl| Patented Jan. 18, 1938 UNlTED STATES CARRIER SUPPLY SYSTEM Robert D. Duncan, Jr., East orange, N. J., as; signor to Wired Radio, Inc., -New York, N. Y., a

corporation of Delaware Application august 1, i936, sel-inl Nogjsaeos 2 claims.

'Ihis invention pertains in general to the transnlission of programs and specifically relates to such systems for transmitting programs in which the-carrier frequency is substantially eliminated 5 'during transmission and replaced upon reception.

The principal object of the invention con? A. Vfurther object of the invention comprises lo providing a suppressed carrier transmission system in which an auxiliary higher ,carrierfrequency is transmitted to the point of reception for incorporation with the received energy for carrier frequency replacement purposes.

These and other objects will be apparent from the following, reference being had to the accompanying drawing which represents one embodiment of the system of my invention.

My invention contemplates the provision of a transmission system for developing a plurality of related carrier frequencies from a master oscillator. These carrier frequencies, having a multiple relationship, are each subjected to individual program modulation. Concomitantly, each of. thecarrier frequencies is eliminated so' that the energy impressed uponthe transmission medium comprises program modulatedl carrier energy in the side band regions, the side band4 regions corresponding to the related carrier fre- ,35 quencies being, of course, discretely situated along the frequency spectrum 'to'produce independent program channels; In. theembodiment illustrated, I employ a commercial power network as the transmission medium, although the invention 40 ls not to be strictly limited thereto, since other media may be employed` without departing from the intended scope of the inventiomv In carrying out the invention, 'the transmitted program energy may be restricted tobut a single side band of frequencies, when desired.

lin accordance with the invention', means are` provided for developing,from the master oscillator, an additional carrier frequency arranged'substantially higher than those .of the program channels. This high carrier frequency is then transmitted over the transmission medium in an unmodulated condition. At the point of reception,

the receiving equipment selectively receives any one of the program channels. At the same time, equipment is provided for the reception of the auxiliary high 4range carrier frequency which operates through means for producing 'the desired lower frequencies for carrier replacement purposes. 'This replacement carrier isvthen incorporated with the received program energy to re- 5 place the suppressed carrier for audible reproduction of the transmitted program.

Referring to the drawing in detail, there is provided a commercial power transmission network I connected with power equipment 2. equipment 2," may be located in the commercial power substation 3. The lines I, equipment 2. and sub-station 3 are indicative of a power transmission network in general. In the present instance, the lines I are of the three phase -cycle 15 alternating current type and operate through a step down transformer 4 to supply commercial voltages to the consumers local transmission circuit 5.

In accordance with the invention, a master os'- '20 cillator 8 develops high frequency oscillations of a standard frequency, such as 13 kilocycles. The

' oscillator 8 may be of a. type known in the art,

such as a crystal controlled thermior'lic oscillator circuit.- 'I'he output of the oscillator 8 is directedr 25 to a harmonic generator 9 which develops, from the master frequency, a plurality of harmonicallyrelated multiple frequencies. vFor example, these multiple frequencies may be 26, 39 and 52 kilocycles, respectively, and correspond to dierent '30 program channels. These different carrier frequencies are respectively. directed to transmitters III, II and I2. The transmitters I0, -II' and I2 each comprise known means for respectively producing amplied 35 three phase carrier frequency energy. 'Ihe high frequency energy for each transmitter is modulated in accordance with the individual source of modulation" energy` associated with that transmitter. In addition, each carrier frequency ito self is eliminatedifrom the modulated carrier energy so that the output at the transmitter comprises three-phase modulated carrier-energy in the side band range with the carrier frequency itself substantially eliminated.` v. 45

, The circuits for such transmission`\ equipment are known in the art. A' special form 'of such y carrier elimination and transmission circuits may be seen in my copendinlg application, Serial No.

40,526,'as well as in the copending applications 50 This power 10 y The outputs of"transmitters IIJ, II and I2 are directed respectively through filters I4, I5 and I6. These filters limit the output of the transmitters to discrete carrier frequency ranges comprising the different program channels. The output circuits of filters I4, I5 and I6 are directed through capacitive couplings to the lines I.

A harmonic generator I1 is also connected with the master oscillator 8 for developing high frequency oscillations within a range higher than the carrier frequencies `associated with the transmitters I0, II and I2. For example, the harmonic generator I1 may develop a frequency of the order of 78 kilocycles. In suitably amplified form, the output of the harmonic generator I1 is directed through lter I8 which limits the output of the harmonic generator I1 to the desired high frequency, such as '18 kilocycles. The output of the filter I 8 is then directed through capacitive couplings to the power lines I.

The consumers dwelling including the circuit 5 is provided with a receiver 20 and loud speaker unit 2I for audibly reproducing the programs transmitted over the lines I.l The receiver embraces suitable selection, amplification and detection circuits known in the art for reproducing desired programs. 'Ihe circuits of receiver 20 include electron tubes energized through power connections 22 extending to the circuit 5. The signal input circuit for the receiver 20 is directed through capacitive couplings 23 and also connected with the power circuit 5.

A further circuit is provided from the capacitive couplings 23 to direct signaling energy through a filter 24 to a multivibrator 25. The filter 24 comprises a selective circuit corresponding to the lter I8 and restricted to the range of high frequency auxiliary carrier such as 78 kilocycles developedby the harmonic generator I1. The multivibrator 25 comprises circuits known in the art for producing a sub-multiple of the oscillations of a given high frequency. In the present instance, the multivibrator 25 produces a 13 kilocycle frequency which is the sixth sub-multiple of the 78 kilocycle auxiliary carrier frequency, as well as other frequencies which are harmonics thereof.

'I'he output of the multivibrator 25 is directed f to a selective filter 26 having a circuit known in the art for producing a selection among the frequencies directed thereto from the multivibrator.

The circuits of the filter 26 are selectively adjustable for passing any one of several harmonic frequencies,.as for-example, 26 kilocycles, 39vkilo-l cycles, or 52 kilocycles, it being remembered that, in the present embodiment of, the invention, the selection circuits of the receiver 20 are adjustable for the selective reception of carrier frequency energy within similar ranges. Accordinsly. a common control knob 28 is mechanically connected with the adjustable elements of the selection circuits of receiver 2D and the adjustable elements of the circuits of the filter 26 so that the output of the filter 26 always 'corresponds in frequency with the selection of the receiver 20.

The output circuit of the filter 26 is directed through an amplifier 21 and thence to the receiver 20. The circuits of the receiver 20 selectively receive the program modulated carrier frequency energy with the carrier frequency itself suppressed while the output of amplifier 21 supplies this carrier frequency. As a result, the receiver 20 replaces this carrier frequency as supplied from the amplifier 21 so that the desired program can be intelligibly reproduced by the loud speaking device 2|.

In another arrangement of the system of the invention, a frequency sub-divider of any type might besubstituted for the multivibrator 25. Again, a harmonic generator may be substituted for the iilter 26 for producing a selected frequency vfrom the sub-divided frequency.

In another embodiment of the invention, the harmonic generators 9 and I1 may be combined in a single unit so that one harmonic generator serves to produce the carrier frequencies `for the transmitters III-I2, as well as the auxiliary carrier frequency passed through filter I8.

Although I have .shown a preferred embodiment of my carrier supply system, it will be understood that various changes can be made without-'departing from the intended scope of Imy invention. Therefore, I do not desire to limit myself to the foregoing except as may be pointed out in the appended claims.

What I claim as new and original and desire to secure by United States Letters Patent is:

1. In a transmission system in which a plurality of modulated suppressed-carrier highfrequency bands and carrier replacement high frequency waves are transmitted to a receiving point as discrete frequencies, receiving apparatus comprising, a receiver selectively operable to receive any one of said plurality of modulated suppressed-carrier high-frequency bands, means responsive to said replacement carrier waves for supplying to said receiver any one of several replacement carrier frequencies corresponding to the carrier suppressed from said modulated highfrequency bands received by said receiver, and common control means for operating said last mentioned means and said receiver so that when a particular modulation band is received by said receiver, said last mentioned means operates to supply thereto a corresponding replacement carrier frequency for intelligibly reproducing the desired modulation by said receiver.

2. In a transmission system in which a plurality of modulated suppressed-carrier highfrequency bandsfand a carrier replacement wave are transmitted at different frequencies to a receiving point, a receiver selectively operable to receive any one of said pluralityof modulated suppressed-carrier high-frequency bands, a replacement carrier means for receiving said replacement wave and adapted to generate therefrom a plurality of replacement carrier waves corresponding to the carriers suppressed from said bands, and common control means for conjointly operating said receiver to receive a selected band and said replacement means to supply thereto a corresponding carrier wave of the proper frequency for replacement purposes.

ROBERT n. DUNCAN, Jn. 

